Mobile users generally travel between first and second cells in a wireless network. To maintain the quality of a communication connection, the mobile station may be “handed-off” from one base station to another. That is, a serving base station located in the first cell may hand over the connection to a target base station located in the second cell. The target base station may establish a new connection for the mobile user, without any user intervention required.
The handover typically requires the serving and target base stations, and the mobile station undergoing handover, to perform a sequence of actions. These actions may include, but are not limited to, changing the radio channel over which the mobile station can send traffic and exchanging signaling messages. Such actions may interrupt the transmission of data frames between the mobile station and the base stations. Handover processes also require allocating system resources to the mobile station at the target base station. Non-limiting examples of these resources include time slot assignments, frequency allocations, and quality-of-service (QoS) assurances.
There are many concerns regarding the handover of a mobile station between the serving and target base stations; however, the handover drop probability is a key parameter in any measurement of connection-level quality-of-service (QoS) in a wireless network. Minimizing the handover drop probability is often an important objective in the wireless system design.
Various resource reservation schemes have been proposed to reduce the probability of dropped handovers, and to ensure acceptable QoS during and after handover. Examples of such schemes are described in U.S. Pat. No. 7,092,719 and U.S. Patent Application Publication No. 2003/0078046. These references disclose reserving resources exclusively for handover purposes in cells that the mobile station is likely to visit when the mobile station, or an application executed by the mobile station, has been “guaranteed” a certain level of service. These reserved resources can only be used by the corresponding mobile station or application. Another example is the adaptive resource allocation for managing QoS in wireless networks as discussed by Gakhar et al., in “Dynamic Resource Reservation in IEEE 802.16 Broadband Wireless Networks”, 14th IEEE International Workshop on Quality of Service, June 2006, and by Huang et al., in “Adaptive Resource Allocation for Multimedia QoS Management in Wireless networks”, IEEE Transactions on Vehicular Technology, Vol. 53, No. 2, March 2004.
On one hand, reserving the resources in anticipation of a possible handover can improve the handover drop performance. On the other hand, however, it excludes other mobile stations and applications from using those resources. That is, other calls or other multimedia data sessions cannot use the resources that are reserved for the handover of a mobile station, even if the mobile station does not actually use the for handover.